1. Field of the Invention
The present invention relates to a sequence controller for a host device and a monitoring device connected with each other on the basis of DVI (Digital Visual Interface) standard, and more particularly, to a controller adapted to ascertain, when the host device and the monitoring device are connected with each other through optical extension cables each based on DVI standard, whether these host device and monitoring device have been exactly connected with each other through the optical extension cables or not as well as to ascertain whether a power from an external power source or supply has been supplied to attached circuits of the host device and the monitoring device or not.
2. Description of the Related Art
In recent years, DVI standard is used in case of digitally transmitting a video signal from a host device (for example, a computer) to a monitoring device (for example, a device including a liquid crystal display (LCD)). The DVI standard adopts a digital transmission system called T.M.D.S. Briefly explaining, the host device has, for example, a T.M.D.S. transmitter and a DVI connector provided therein and the monitoring device has a T.M.D.S. receiver and a DVI connector provided therein, and the DVI connector of the host device is connected to the DVI connector of the monitoring device through extension cables each based on the DVI standard. A video signal digitally produced in the host device is transmitted from a video controller of the host device through the T.M.D.S. transmitter and the DVI connector to the extension cables, and in the monitoring device, the digital video signal is received by the T.M.D.S. receiver and sent therefrom to a display controller in which the received digital signal is processed to obtain a signal adapted for a display of the monitoring device. Then, the signal is sent to a display driver to display a picture or image corresponding to the digital video signal on the display.
Here, DVI is an abbreviation for Digital Visual Interface as mentioned above, and one of interface standards defined by DDWG (Digital Display Working Group) which is an organization of computer industry for the purpose of digitally transmitting a video signal to be supplied to a liquid crystal display, cathode ray tube display, and the like. T.M.D.S. is an abbreviation for Transition Minimized Differential Signaling, which is a digital transmission system for video signals developed by Silicon Image Company Ltd, in U.S. A. and transmits a serial digital signal by differential driving by use of two signal lines. As is well known, in DVI standard, one color component signal of a color video signal is transmitted using one channel of T.M.D.S., and all color component signals, namely, R (red) component signal, G (green) component signal, and B (blue) component signal of the color video signal using three channels of T.M.D.S. In addition thereto, one channel of T.M.D.S. is used for transmission of clock.
In case of connecting the host device and the monitoring device with each other through the extension cables (metal extension cables, optical extension cables or the like) each based on DVI standard as described above, it is necessary to ascertain whether the host device and the monitoring device are exactly connected with each other through the extension cables or not. In general, DDC is used to ascertain whether both devices are exactly connected with each other. DDC is a standard defined by VESA in U.S. A. for the purpose of realizing Plug and Play of a display. Further, VESA is an abbreviation for Video Electronics Standards Association, and DDC is an abbreviation for Display Data Channel. Plug and Play (PnP) of a display is a system in which when a display is connected to a host device, OS (operating system) of the host device automatically detects the display and the optimum setting therefor is automatically carried out without manual setting work by a user. In order to materialize this Plug and Play of a display, DDC standard uses three signals of DDC data, DDC clock, and DDC+5V (DC voltage of +5V).
FIG. 10 is a flow chart showing one prior art process for ascertaining whether a host device and a monitoring device are exactly connected with each other or not by use of DDC standard. Since DDC data and DDC clock are low speed signals, and DDC+5V signal and HPD signal that is a return signal of the DDC+5V signal are direct current signals, these signals are transmitted and received via metal extension cables each based on DVI standard, though not shown.
As shown in FIG. 10, at first, a (DDC+5V) signal source provided in the host device (for example, computer) H is caused to turn on in a step 11, and in the next step 12, a (DDC+5V) signal is outputted from the (DDC+5V) signal source and is transmitted to the monitoring device M via a metal extension cable based on DVI standard. In the monitoring device M, it is determined in a decision step 23 whether the transmitted (DDC+5V) signal is the proper (DDC+5V) signal or not. In case it is the proper (DDC+5V) signal, the decision step 23 outputs “Yes” signal, and the process proceeds to a step 22. In the step 22, a HPD signal (a return signal of the (DDC+5V) signal) is generated from a HPD signal source (not shown) provided in the monitoring device M, and is transmitted to the host device H via a metal extension cable based on DVI standard. The HPD signal transmitted to the host device H is determined whether it is the proper HPD signal or not in a decision step 13 of the host device H. In case it is the proper HPD signal, the decision step 13 outputs “Yes” signal, and in the next step 14, a sequence for digitally transmitting a video signal is started.
Further, HPD is an abbreviation for Hot Plug Detect, is established by VESA, and is a standard for enabling a display or other peripheral equipment to pull out and/or plug in without turning off the power supply to the host device H and/or the monitoring device M. For example, when a display of the monitoring device M is pulled out from and then plugged in the monitoring device M, the host device automatically detects this fact and newly carries out the plug and play of the display. Accordingly, the fact that the proper HPD signal has been detected in the host device H indicates that the display is exactly connected to the monitoring device M.
Next, there is shown in FIG. 11 one example of the construction of the prior art that uses T.M.D.S. transmission system and optical extension cables in order to digitally transmit a video signal at high speed, and that uses DDC standard and metal extension cables for the purpose of ascertaining whether a host device and a monitoring device are exactly connected with each other or not.
FIG. 11 is a connection diagram showing a connecting manner between a host device H and a monitoring device M. In an interface 1 of the host device H, there are provided three pairs of terminals (six terminals) for transmitting one set of T.M.D.S. data 0 for differential driving corresponding to, for example, R component of a color video signal, one set of T.M.D.S. data 1 for differential driving corresponding to, for example, G component thereof, and one set of T.M.D.S. data 2 for differential driving corresponding to, for example, B component thereof; one pair of terminals (two terminals) for transmitting one set of T.M.D.S. clocks for differential driving; one terminal for transmitting (DDC+5V) signal; one terminal for transmitting and receiving DDC clock; one terminal for transmitting and receiving DDC data; one terminal for receiving HPD signal; and one ground terminal.
On the other hand, in an interface 2 of the monitoring device M, there are provided three pairs of terminals (six terminals) for receiving one set of T.M.D.S. data 0 for differential driving corresponding to R component transmitted from the host device H, one set of T.M.D.S. data 1 for differential driving corresponding to G component, and one set of T.M.D.S. data 2 for differential driving corresponding to B component; one pair of terminals (two terminals) for receiving one set of T.M.D.S. clocks for differential driving; one terminal for receiving (DDC+5V) signal; one terminal for receiving and transmitting DDC clock; one terminal for receiving and transmitting DDC data; one terminal for transmitting HPD signal; and one ground terminal.
In order to digitally transmit T.M.D.S. data 0-2 corresponding to R component, G component, and B component of a color video signal as well as T.M.D.S. clocks at high speed from the host device H to the monitoring device M, an attached circuit 61 of the host device H and an attached circuit 81 of the monitoring device M are connected with each other through four optical extension cables 4-1, 4-2, 4-3, and 4-4. Four transform devices TR1, TR2, TR3, and TR4 are provided in the attached circuit 61 of the host device H, and three devices TR1-TR3 are differentially driven by corresponding sets of T.M.D.S. data 0, 1, and 2 for differential driving, thereby to output serial digital signals, respectively, and the remaining one device TR4 is differentially driven by one sets of T.M.D.S. clocks for differential driving, thereby to output a serial clock. Moreover, to the output circuits of these transform devices TR1, TR2, TR3, and TR4 are connected electric-optic conversion elements, for example, semiconductor laser diodes LD1, LD2, LD3, and LD4, respectively. The transform devices TR1-TR4 and laser diodes LD1-LD4 constitute an electric-optic conversion circuit 15. One ends of the optical extension cables 4-1, 4-2, 4-3, and 4-4 are optically coupled to the laser diodes LD1, LD2, LD3, and LD4, respectively. Thus, the T.M.D.S. data 0-2 corresponding to R, G, B components of a video signal and T.M.D.S. clocks for synchronizing the T.M.D.S. data 0-2 are converted into serial optical digital signals, respectively, by the electric-optic conversion circuit 15, which in turn are transmitted to the monitoring device M through the optical extension cables 4-1 to 44 based on DVI standard.
Likewise, in the attached circuit 81 of the monitoring device M is provided a photoelectric conversion circuit 25 which is constituted by four photoelectric conversion elements, for example, photodiodes PD1, PD2, PD3, and PD4, and four inverse transform devices RTR1, RTR2, RTR3, and RTR4. The photodiodes PD1, PD2, PD3, and PD4 are optically coupled to the other ends of the optical extension cables 4-1, 4-2, 4-3, and 4-4, respectively. The inverse transform devices RTR1, RTR2, RTR3, and RTR4 function to inversely transform electric signals outputted respectively from the photodiodes PD1, PD2, PD3, and PD4 into the original sets of T.M.D.S. data 0, 1, and 2 for differential driving, and the original set of T.M.D.S. clocks for differential driving, respectively. As a result, the serial optical digital signals transmitted from the host device H through the optical extension cables 4-1 to 4-4 are inversely transformed into the original sets of T.M.D.S. data 0, 1, and 2 for differential driving, and the original set of T.M.D.S. clocks for differential driving, respectively, by the photoelectric conversion circuit 25, and then they are sent to the interface 2. Further, stabilized power supply voltages are supplied to the four transform devices TR1, TR2, TR3, and TR4 of the attached circuit 61 of the host device H and to the four inverse transform devices RTR1, RTR2, RTR3, and RTR4 of the attached circuit 81 of the monitoring device M through regulators 17 and 27, respectively.
In order to ascertain whether the host device H and the monitoring device M are exactly connected with each other or not by use of DDC standard, a (DDC+5V) transmitting terminal of the interface 1 of the host device H and a (DDC+5V) receiving terminal of the interface 2 of the monitoring device M are directly connected with each other through a metal extension cable 5-1 based on DVI standard, and a HPD signal receiving terminal of the interface 1 of the host device H and a HPD signal transmitting terminal of the interface 2 of the monitoring device M are directly connected with each other through a metal extension cable 5-4 based on DVI standard. In addition, in order to transmit and receive DDC data and DDC clocks, a DDC clock transmitting/receiving terminal and a DDC data transmitting/receiving terminal of the interface 1 of the host device H are connected to a DDC clock transmitting/receiving terminal and a DDC data transmitting/receiving terminal of the interface 2 of the monitoring device M, respectively, through a buffer circuit 16 provided in the attached circuit 61 of the host device H, metal extension cables 5-2 and 5-3 each based on DVI standard, and a buffer circuit 26 provided in the attached circuit 81 of the monitoring device M. Further, a ground terminal of the interface 1 of the host device H and a ground terminal of the interface 2 of the monitoring device M is directly connected with each other through a metal extension cable 5-5 based on DVI standard.
As shown in FIG. 11, in a case arranged such that a video signal is digitally transmitted at high speed through the optical extension cables by use of T.M.D.S. transmission system, and that (DDC+5V) signal, DDC clock, DDC data and HPD signal all of which are low speed signals for carrying out the plug and play of a display are transmitted through the metal extension cables, an external power source or supply is naturally required to drive the electric-optic conversion circuit 15, the buffer circuit 16, and the photoelectric conversion circuit 25, the buffer circuit 26 provided in the attached circuits 61 and 81, and other attached circuits, etc. In order to ascertain whether the external power source supplies its power to these circuits without fail or not, in the prior art, a control for ascertaining whether the external power source supplies its power to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc. without fail is added to the control for ascertaining whether the host device H and the monitoring device M are exactly connected with each other by use of DDC standard as shown in the flow chart of FIG. 10.
FIG. 12 is a flow chart showing one example of the prior art in which the aforesaid control for ascertaining whether the external power source supplies its power to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc. without fail is added to the flow chart of FIG. 10. Further, the control for ascertaining whether the host device H and the monitoring device M are exactly connected with each other by use of DDC standard has been already described with reference to FIG. 10, and the explanation thereof will be omitted here.
As shown in FIG. 12, at first, an external power source is caused to turn on in a step 3, and in the next decision step 31, it is determined whether the external power source has been turned on or not. In case the external power source has been turned on, the decision step 31 outputs “Yes” signal, and the process proceeds to a step 32. In the step 32, a predetermined power from the external power source is supplied to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc. In this manner, it is ascertained that the external power source is supplying its power correctly to these circuits.
Though the prior art ascertains that the external power source is supplying its power correctly to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc. on the basis of the above-mentioned process, it is impossible to ascertain whether the host device H and the monitoring device M are exactly connected with each other through the optical extension cables 4-1 to 4-4 each based on DVI standard. If the host device H should not be connected exactly to the monitoring device M through the optical extension cables 4-1 to 4-4, even the external power source is caused to turn on thereby to supply its power to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc., any video signal is not transmitted from the host device H to the monitoring device M, and hence it is impossible to display a picture or image corresponding to the video signal on the display. Accordingly, there is incurred a result that the power is wasted.
Moreover, the optical extension cables 4-1 to 4-4 and the metal extension cables 5-1 to 5-5 are usually constructed as a composite cable in one body. Accordingly, if the metal extension cables 5-1 to 55 have been exactly connected, then the optical extension cables 4-1 to 4-4 would have been exactly connected without fail. For this reason, as already discussed with reference to FIG. 10, when it is ascertained that the host device H and the monitoring device M are exactly connected with each other by carrying out the process for ascertaining whether the host device H and the monitoring device M are exactly connected with each other by use of DDC standard, there occurs a drawback that the sequence for digitally transmitting a video signal is started even if the external power source does not supply its power to the electric-optic conversion circuit 15, the buffer circuit 16, the photoelectric conversion circuit 25, the buffer circuit 26, etc.